A scan type radar apparatus that detects an object or the like may be used in a monitoring system or the like. For example, a radio radar apparatus, such as an FM-CW (Frequency Modulated-Continuous Wave) radar apparatus or the like, periodically changes the transmission wave frequency and carries out the transmission without intermission. Because the transmission wave frequency is changed by the time the reflected wave from a detection target is received, the distance from the FM-CW radar apparatus to the detection target and a moving velocity of the detection target may be detected by measuring a difference between the transmission wave frequency and the reflected wave frequency in order to measure a time delay of the reflected wave. For this reason, when the FM-CW radar apparatus is used in a traffic monitoring system, for example, and the number of vehicles and the velocity of the vehicles traveling on each lane of the road monitored by the FM-CW radar apparatus are detected, it is possible to detect the degree of traffic congestion on each lane of the road. It is also possible to control a traffic light depending on the degree of traffic congestion, and to detect an obstructing object, such as trash, existing on the lane and warning drivers by displays or the like.
The FM-CW radar apparatus detects the detection target by pairing a difference between the transmission wave and the reflected wave within a frequency raising interval, and a difference between the transmission wave and the reflected wave within a frequency lowering interval. For example, a detection result of a number of pairs within a predetermined time may be output with a predetermined format. For this reason, when the number of pairs becomes extremely large as a result of the pairing, data of the detection target are desirably transferred at a relatively high transfer rate (or bit rate). However, the time and cost required to develop such a radar apparatus capable of transferring the data at the high transfer rate would increase, thereby making it difficult to create a relatively inexpensive radar apparatus.
On the other hand, in a case in which the transfer rate of the data of the detection target may be relatively low, only a limited number of detection targets (that is, the number of pairs) may be detected within a predetermined time. For this reason, when a relatively inexpensive radar apparatus having a relatively low data transfer rate, such as an on-board radar apparatus for vehicles, is used for the traffic monitoring system, the cost and time required to develop the radar apparatus may be prevented from increasing, however, only a limited number of detection targets becomes detectable.
Accordingly, a method has been proposed to assign a priority order, such as a detecting order, for example, with respect to the detection results, in order to output the detection results starting from the detection result having the highest priority order. However, even when the priority order is assigned with respect to the detection results, it is still only possible to detect a limited number of detection targets, regardless of the data transfer rate of the radar apparatus.
Accordingly, in the conventional radar apparatus, because only a limited number of detection targets may be detected, it is difficult to detect the detection targets with a high accuracy.
The applicant is aware of Japanese Laid-Open Patent Publication No. 2010-231604 and Japanese Laid-Open Patent Publication No. 9-190593.